De arts zei dat ik moest gaan zitten als ik weer duizelig of misselijk werd.

Arts is a slightly more formal word for doctor/physician. Dokter is the more common everyday word in speech.

In many situations, they refer to the same person:

• de arts = the physician, doctor
• de dokter = the doctor

So here de arts zei... sounds a bit more formal or written.

After dat in Dutch, you usually get a subordinate clause, and subordinate clauses have different word order from main clauses.

Compare:

• Main clause: Ik moet gaan zitten.
• After dat: ...dat ik moest gaan zitten.

In a subordinate clause, the subject usually comes before the verbs, and the verbs move toward the end of the clause.

So:

• De arts zei = main clause
• dat ik moest gaan zitten = subordinate clause

That is why the structure looks different from English.

Moest is the simple past form of moeten.

The forms are:

• ik moet = I must / have to
• ik moest = I had to / was supposed to

Dutch modal verbs often have irregular past forms, so you just have to learn them:

• kunnen → kon
• mogen → mocht
• moeten → moest
• willen → wilde / wou

So ik moest is the correct past form.

Dutch moeten often covers ideas that English expresses with must, have to, or sometimes should, depending on context.

Here, De arts zei dat ik moest gaan zitten means the doctor instructed or told the speaker to sit down. In English, you might translate that as:

• I had to sit down
• I was supposed to sit down
• I should sit down

Dutch often uses moeten for this kind of reported instruction.

Gaan zitten literally means go sit or go and sit, but in natural English it usually just means sit down.

It is a very common Dutch expression:

• Ga zitten. = Sit down.
• Ik ging zitten. = I sat down.
• Ik moest gaan zitten. = I had to sit down.

So gaan does not always mean physical movement from one place to another. In combinations like this, it helps express the start of an action.

After a modal verb like moeten, Dutch normally uses the bare infinitive, without te.

So you get:

• ik moet gaan zitten
• ik kan komen
• ik wil eten
• ik mag blijven

Not:

• ik moet te gaan zitten ❌

So moest gaan zitten is correct because moeten is followed directly by infinitives.

Because this is a verb combination:

• gaan
  • infinitive-like action expression
• zitten as part of the expression gaan zitten

Together they mean to sit down.

Dutch often builds meanings with multiple verbs, especially after modal verbs:

• ik moest gaan zitten
• ik wilde blijven wachten
• ik kon niet meer slapen

So the sentence ends with a small verb cluster, which is very normal in Dutch.

Here als is best understood as if.

• als ik weer duizelig of misselijk werd = if I became dizzy or nauseous again

It gives a condition: if that happened, then I was supposed to sit down.

In some contexts, als can also be translated as when, but here if is the most natural interpretation because it refers to a possible future situation viewed from the past.

Weer usually means again.

So:

• duizelig werd = became dizzy
• weer duizelig werd = became dizzy again

It comes before the adjective it affects. Here it applies to the possible return of the symptom:

• weer duizelig
• weer misselijk

The sentence means the doctor was talking about the symptoms coming back.

These are two different symptoms:

• duizelig = dizzy
• misselijk = nauseous / sick to your stomach

So:

• ik ben duizelig = I am dizzy
• ik ben misselijk = I feel nauseous

They are often used in medical contexts, so this is very useful vocabulary.

Yes. Werd is the simple past of worden.

Here worden means to become, not the passive auxiliary.

So:

• ik word duizelig = I become / am getting dizzy
• ik werd duizelig = I became / was getting dizzy

In this sentence:

• als ik weer duizelig of misselijk werd

means:

• if I became dizzy or nauseous again

So werd is being used in the sense of became.

Because both adjectives belong to the same verb.

So this structure means:

• duizelig of misselijk werd = became dizzy or nauseous

Dutch does not need to repeat the verb:

• als ik weer duizelig of misselijk werd
• not als ik weer duizelig werd of misselijk werd, although that would still be understandable

Using one verb for both adjectives is more natural and efficient.

Because als also introduces a subordinate clause, and in subordinate clauses the conjugated verb usually goes to the end.

So:

• als ik weer duizelig of misselijk werd

has this structure:

• als = if
• ik = subject
• weer duizelig of misselijk = rest of the clause
• werd = verb at the end

This is one of the most important Dutch word-order patterns to get used to.

Yes, but the meaning changes slightly.

• ik moest gaan zitten = I had to sit down
• ik moest zitten = I had to be sitting / I had to remain seated

So gaan zitten focuses on the action of moving into a seated position.
That fits this context better: if the speaker started feeling bad again, the doctor advised them to sit down.

Yes. It combines several very common Dutch patterns:

1. reporting speech

   • De arts zei dat...

2. a modal verb

   • ik moest...

3. a multi-verb expression

   • gaan zitten

4. a conditional subordinate clause

   • als ik weer duizelig of misselijk werd

So even though the sentence looks long, it is built from very standard Dutch grammar.